Hippotherium malpassii (Equidae, Mammalia) from the latest Miocene (late Messinian; MN13) of Monticino gypsum quarry (Brisighella, Emilia-Romagna, Italy)

ISSN 0375-7633 doi:10.4435/BSPI.2013.12 rbernor@howard.edu

KEY WORDS - Hippotherium, dentition, postcranial skeleton, Messinian, Brisighella, Italy.

ABSTRACT - We describe the Hippotherium record from the latest Miocene (MN13) vertebrate faunal assemblage of the Monticino gypsum quarry (also known as Brisighella). This small sample would appear to be attributable to a single species of hipparionine horse. The referral to the recently described species Hippotherium malpassii Bernor, Kaiser, Nelson & Rook, 2011 would appear to be the best one possible. The Monticino gypsum quarry specimens correspond to the size of Hippotherium malpassii and show a suite of morphological features that allow their specific attribution. Formal description of the Brisighella hipparion specimens augments the previous knowledge of the Monticino gypsum quarry vertebrate fauna, one of the best-known latest Messinian fossil assemblages of continental Europe.

RIASSUNTO - [Hippotherium malpassii (Equidae, Mammalia) dal Miocene terminale (Messiniano superiore; MN13) della Cava di gessi del Monticino (Brisighella, Emilia-Romagna, Italia)] - Vengono descritti i resti fossili di Hippotherium della associazione faunistica del Miocene terminale (MN13 nella biocronologia continentale a mammiferi dell’Europa) proveniente della Cava di gessi del Monticino (nota anche come fauna di Brisighella). Il campione è rappresentato da un numero limitato di resti, tutti riferibili ad una singola specie di ippoterio. Il campione è attribuito alla specie Hippotherium malpassii Bernor, Kaiser, Nelson & Rook, 2011, recentemente descritta sulla base dell’abbondante campione fossile proveniente dal bacino di Baccinello-Cinigiano, in provincia di Grosseto. In base alle dimensioni, i resti della Cava di gessi del Monticino corrispondono alla taglia della specie Hippotherium malpassii. Questa attribuzione è inoltre supportata dalla presenza di una serie di tratti morfologici caratteristici. La descrizione formale dell’ippoterio di Brisighella espande la nostra conoscenza sulla fauna della Cava di gessi del Monticino, una delle associazioni faunistiche a mammiferi del Messiniano terminale meglio conosciute in Europa. A conclusione della descrizione morfologica del piccolo campione di Hippotherium di Brisighella viene infine discussa la peculiare distribuzione del record fossile dei perissodattili nel quadro della località a mammiferi del Miocene Superiore della Penisola Italiana.

INTRODUCTION

The occurrence of a rich late Messinian fossil

vertebrate assemblage in karst sediments associated with

the Messinian evaporites in the Monticino gypsum quarry

near Brisighella (Emilia-Romagna, Central Italy; Fig. 1)

was first reported by Costa et al. (1986). According to local

and regional geological constraints (Marabini & Vai, 1989;

Vai, 1989), the vertebrate assemblage is correlated with

the late Messinian Stage and European Land Mammal

Age (ELMA) MN13. The vertebrate fauna has been the

subject of a number of descriptive papers (De Giuli et

al., 1988; De Giuli, 1989; Kotsakis, 1989; Kotsakis &

Masini, 1989; Masini, 1989; Masini & Thomas, 1989;

Torre, 1989; Rook et al., 1991; Rook, 1992; Masini &

Rook, 1993; Rook & Masini, 1994; Delfino, 2002; Rook,

2009; Gallai & Rook, 2011).

Soon after the 1985 discovery of the paleontological

site within the gypsum quarry, a proposal was advanced

to create an open-air geo-paleontological museum at

Brisighella (Vai, 2007). Between 2001-2004, the first

preservation activities at the site were undertaken thanks

to an agreement between the Regional Administration

(Regione Emilia-Romagna) and the Town Administration

(Comune di Brisighella), and an open-air museum of the

quarry area was realized in 2005-2006. A geo-park with

a 14.5 hectare environmental refuge was soon created for

a variety of didactic activities, and opened to the general

public in 2007 (Sami, 2007a, b).

In this paper we report on the unpublished fossil

remains of a tridactyl horse (Hippotherium) from the

Monticino gypsum quarry. This taxon, represented

by limited fossil material, has not been yet formally

described, although its recovery dates back to the time

of the Brisighella fauna’s discovery (De Giuli et al.,

1988). The identification of this sample has important

biochronologic and biogeographic implications. We also

provide a discussion of the significance of the hipparion

record in the Messinian of Italy.

GEOLOGICAL SETTING

The exposed succession within the Monticino gypsum

quarry (Fig. 1) is composed, at the base, of a series of

tilted gypsum layers with interbedded clays of the early

Messinian Gessoso-Solfifera Formation. The gypsum

was slightly eroded and subjected to a karst dissolution

cycle that took place following the tectonic tilting of

the strata. The deposits that infill the net of fissures

intersecting the gypsum and the depressions on the upper

surface of the gypsum sequence consist of marly-clays,

fine grained conglomerates and sand lenses derived from

the Colombacci Formation (grey pelites and variegated

marly clays with whitish to yellow thin evaporitic marly

limestone; latest Messinian in age). They contain partially

articulated and fragmented skeletons of large mammals,

and very abundant microvertebrate remains. Several

fossiliferous collecting points have been identified along

the Monticino gypsum quarry outcrop (Fig. 2), some

of which represent successive sampling of the same

fissure that were brought to light by the progress of the

quarrying activity. The Gessoso-Solfifera Formation is

unconformably overlain by a thin discontinuous layer

of greenish to blackish clay (0 to 1 m thick) that is

considered equivalent to the later depositional phases of

the Colombacci Formation and is correlated with the late

Messinian. The succession is capped by up to 20 m of

Early Pliocene marine gray marly clays (Argille Azzurre

Formation) whose base falls in the Sphaeroidinellopsis

Zone, and which overlie, with apparent conformity, the

Colombacci Formation. We refer the reader to Vai (1989)

for a more complete discussion of the geological setting

of the Romagna Apennine, and to Marabini & Vai (1989)

for further details on the geology of the Monticino gypsum

quarry.

MATERIALS AND METHODS

Studied Material

The described specimens from Monticino gypsum

quarry are housed in the MSF, whereas the comparative

sample includes material from Baccinello V3, housed at

the IGF and NHMB (see acronyms below).

Institutional Acronyms

“MSF” indicates the Museo Civico di Scienze Naturali

“Malmerendi”, Faenza, “IGF” denotes the Museo di Storia

Naturale (Sezione di Geologia e Paleontologia) of the

Università di Firenze, and “NHMB” refers to the Basel

Naturhistorisches Museum (Switzerland).

Fossil Site Acronyms

“BRS” indicates the fossiliferous locality

(=Brisighella); the number following the acronym

(e.g., BRS 25) indicates the single karst fissure (Fig. 2),

whereas when a second number follows (e.g., BRS 25/1)

it indicates the specimen field catalogue number. “BCB

V3” refers to Baccinello V3 (latest Messinian, Tuscany;

Benvenuti et al., 2001; Rook et al., 2011).

Measurements

We have measured the upper and lower dentitions

using standard equid measurements published by

Eisenmann et al. (1988) and Bernor et al. (1997). The third

metacarpal (MCIII) is too fragmentary to measure, but its

general size is comparable to Hippotherium malpassii.

Measurements of the Brisighella hipparion specimens are

provided in Appendix, while teeth metrical comparison

and species descriptive statistics are offered in Tab. 1.

Measurement numbers (M1, M2, M3, etc.) refer to those

published by Eisenmann et al. (1988; and rounded to 0.1

mm) for postcranium (also in Bernor et al., 1997), whereas

tooth measurement numbers refer to those published

by Bernor et al. (1997), Bernor & Franzen (1997) and

Bernor & Harris (2003). The osteological nomenclature

has been adapted from Nickel et al. (1986). Getty (1982)

was also consulted for morphological identification and

comparison.

Fig. 1 - Location map (left) and outline of the geological section outcropping in the Monticino gypsum quarry (center), with formal geological units (Formations) and chronologic setting of the exposed sediments (right). The fossils vertebrates of the Monticino gypsum quarry faunal assemblages are found in the Colombacci Fmt., the deposition of which is tightly placed in time by the constraints of the geological setting. The Colombacci Fmt. is deposited on the karstic surface of the Messinian gypsum (thereafter the infra-Messinian tectonic phase that affected the Gessoso-solfifera Fmt.), and is capped as an angular conformity by the earliest Pliocene marine clays of the Argille Azzurre Fmt. (Zanclean). Modified after Marabini & Vai (1989).

Fig. 2 - Scheme of the fossil collecting sites within the Monticino gypsum quarry outcrop. Sites that yielded Hippotherium are highlighted by circled numbers on a coloured background (after a sketch by M. Sami, modified from Rook & Delfino, 2007).

Taxonomic remarks

The genus nomen Hipparion has been used in a

variety of ways by different authors. Here we follow the

systematics recently provided by Bernor et al. (1996, 1997,

2011) for hipparionine horse superspecific taxa.

SYSTEMATIC PALEONTOLOGY

Suborder H

Wood, 1937

Superfamily e

Hay, 1902

Family e

Gray, 1821

Subfamily e

Steinmann & Doderlein, 1890

Tribe H

Quinn, 1955

Genus Hippotherium Kaup, 1832

Hippotherium malpassii Bernor, Kaiser, Nelson & Rook, 2011

(Figs 3-5)

1988 Hipparion sp. de Giuli et al., p. 68. 1993 Hipparion sp. masini & Rook, p. 80. 2004 Hipparion sp. Rook & delfino, p. 194. 2007 Hipparion sp. Rook & delfino, p. 118.

Material examined - The Monticino gypsum quarry

Hippotherium sample comprises five specimens: MFS119,

left P

_{(Fig. 3a); MFS120, left P}

_{(Fig. 3b); BRS 15/1,}

upper molar; MSF122, left M

(Fig. 4); MSF121,

fragmentary left Metacarpal III (Fig. 5).

postfossettes have complex mesial and distal borders,

but in particular the distal border of the prefossette; they

have a very large, single pli; they have lenticular shaped

protocones; the protocone is placed well lingual of the

hypocone; the hypoglyph is deeply incised; the parastyle

and mesostyle are narrow loops. The plications of the

pre- and postfossettes are not as complex as some of the

Baccinello sample, but this may be due to their relatively

early stage of wear. Both of these teeth have paracone

labial enamel borders that are high and round and equal

to score #2 of Mihlbachler et al. (2011) and Wolf et al.

(2012), which has the effect of producing a deep-wide

groove across the mesostyle-protocone portion of the

crown. As such, it may be inferred that this horse had a

low abrasive diet (= large browse component) and was

likely a mixed-feeder at the browsing end of the

browser-grazer spectrum.

The lower molar, MSF122 (Fig. 4), is a left M

with

a crown height of 32.3 mm. This specimen is in middle

adult wear and has the following salient characters: the

metaconid and metastylid are round; pre- and postflexids

are labiolingually compressed and have simple margins;

linguaflexid has a deep U-shaped morphology; ectoflexid

is deep, fully penetrating the metaconid-metastylid

junction; protoconid and metaconid have rounded

margins; there is no evidence of an ectostylid or a pli

caballinid; protoconid raises only about 23 mm from the

base of the crown and is pointed at its tip.

There is a fragmentary metacarpal III (Fig. 5) that

includes a portion of the proximal end and the fragmentary

anterior two-thirds of the shaft. The specimen is too

fragmentary to measure but, in general, would appear to

have dimensions and proportions similar to the Baccinello

sample of Hippotherium malpassii (see Appendix).

As an assemblage, this would appear to be material

of a single species of hipparionin horse. The referral to

Hippotherium malpassii would appear to be the best

one possible. It is the size of Hippotherium malpassii

type material (Tab. 1; Fig. 6) and has a constellation

of morphological features that best fit this taxon:

there is no ectostylid or pli caballinid typical of Late

Miocene - early Pliocene Eurygnathohippus; neither the

metaconid nor metastylid is pointed as is often the case in

Eurygnathohippus; it is neither very large as in Sivalhippus

nor very small as in Cremohipparion; the MCIII does

not have either massive proportions as is often seen in

Sivalhippus, nor extremely gracile proportions as seen

in Hipparion or Cremohipparion. In sum, the Brisighella

hipparion is best referred to Hippotherium malpassii

recently described from Baccinello (Bernor et al., 2011).

M1 20.8 9 22.5 20.7 25.1 1.70 ±1.11 M2 19.5 6 21.2 19.7 22.4 1.06 ±0.85 M3 13.8 10 12.2 11.3 13.4 0.67 ±0.42 M4 6.7 10 6.8 4.7 8.4 1.16 ±0.72 M5 7.7 10 8.4 6.4 10.6 1.30 ±0.81 M6 13.6 8 11.4 8.2 14.9 2.24 ±1.55 M7 11.9 7 12.4 9.3 13.3 1.41 ±1.05 M8 11.4 10 10.7 9.5 12.1 0.95 ±0.59 M9 10.3 8 10.0 8.8 11.7 0.95 ±0.66 M10 32.3 7 35.8 25.6 45.7 7.88 ±5.84 Tab. 1 - Hippotherium P4 _{and M}

2 (see Appendix for metrical

variables explanation) from Monticino gypsum quarry compared to descriptive statistics of Hippotherium malpassii from type locality (Baccinello V3).

CONCLUSIONS

The Monticino gypsum quarry (Brisighella) karst

fissure fillings complex yielded very few horse remains

documented from five collecting sites (BRS 1, BRS 3,

BRS 5, BRS 15, BRS 25), described herein for the first

time. On the basis of morphological and morphometric

comparisons we attribute the Brisighella sample to

Hippotherium malpassii, a species recently described from

the Late Miocene (Messinian) of Baccinello V3 in southern

Tuscany (Bernor et al., 2011).

The Italian Late Miocene Hippotherium record,

although relatively poor, contributes to our knowledge of

the peculiar paleobiogeographic evolution of the Italian

Peninsula. During Late Turolian (Late Miocene, MN12

time equivalent), no equid (nor any perissodactyls)

are known in Italy either from the so-called V2 faunal

assemblages of the Tusco-Sardinian bioprovince (Monte

Bamboli in Tuscany and Fiume Santo in Sardinia; Rook

et al., 1999, 2006; Bernor et al., 2001; Chesi et al., 2009)

or from the faunas of the Abruzzi Apulian bioprovince

(Abbazzi et al., 1996; Rook et al., 2006).

The faunal turnover that characterized the continental

peninsular Italy during the latest Miocene led to the

extinction of all taxa typical of the Tusco-Sardinian

area and was characterized by the dispersal of a faunas

composed by continental European taxa, characterizing

the latest Miocene Italian mammal assemblages, along

the northern Apennines, from Piedmont (Ciabot Cagna,

Fig. 4 - Left M2 of Hippotherium malpassii from Monticino gypsum

quarry (Brisighella). MSF122 in occlusal (a), labial (b), lingual (c), mesial (d), and distal (e) views. Scale bar = 3 cm.

Fig. 3 - Left P4 _{of Hippotherium malpassii from Monticino gypsum quarry (Brisighella). a) MSF119 in distal (a1), mesial (a2), occlusal (a3),}

labial (a4), and lingual (a5) views. b) MSF120 in distal (b1), mesial (b2), occlusal (b3), labial (b4), and lingual (b5) views. Figures a5 and b5 illustrate the broad labio-lingual groove across the mesostyle-protocone portion of the tooth. Scale bar = 3 cm.

Verduno and Moncucco; Cavallo et al., 1993; Angelone

et al., 2011; Colombero & Pavia, 2013) to Romagna

(Brisighella, this paper) and southern Tuscany (Borro

Strolla, Baccinello V3, etc.; Rook et al., 2006; Abbazzi et

al., 2008). Perissodactyla were part of this renewed fauna,

including tapirs (Rook & Rustioni, 1991), rhinos (Hürzeler

& Engesser, 1976; De Giuli et al., 1998) and hipparions

(Bernor et al., 2011; this paper). The MN13 record of the

Hippotherium record in Italy is the youngest known for

this lineage in Eurasia.

In the light of the renewed interest in the Italian

Hippotherium record (Bernor et al., 2011; this paper), a

revision of the hipparion sample from Casino - only in

part figured by Forsyth Major (1875, 1877) and by Pirlot

(1956), and generally referred to as part of the “Hipparion

gracile group” (among others Alberdi, 1986; Forsten,

2002) - would be most welcome, given its possible

identification as representing a form close to the species

Hippotherium malpassii.

Fig. 6 - Bivariate plot of P4 _{measurements. Protocone width (M11)}

is plotted versus protocone length (M10). BRS specimens (asterisks) are compared with a sample of Late Miocene Old World hipparions: Baccinello V3, Italy (open triangle); Gaiselberg, Austria (solid star); Höwenegg, Germany (cross circled); Sinap, Turkey (cross boxed); Baltavar, Hungary (diamond). Comparative data derived from Bernor et al. (1997, 2011).

Fig. 5 - Left metacarpal III of Hippotherium malpassii from Monticino gypsum quarry (Brisighella). MSF121 in cranial (a), caudal (b), proximal (c), lateral (d), and medial (e) views. Scale bar = 5 cm.

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ACKNOWLEDGMENTS

We wish to thank Tonino Benericetti from Zattaglia for the patient and careful activity on the Monticino fossiliferous locality, as well as Gian Paolo Costa, and Marco Sami (Faenza) for constructive discussions. Finally we would like to acknowledge the Cultural Heritage service of the Town Administration for facilitating access to fossil material in the collections of the Faenza Museum. This contribution is part of a broader research program on Late Neogene vertebrate evolution developed at the University of Florence (coordinator L.R.). We would like to acknowledge financial support for his research from the National Science Foundation: EAR0125009, EAR113175 (to RLB) and BCS-0321893 (grant made to F.C. Howell and T.D. White; RHOI, University of California at Berkeley). Thanks are extended to M. Delfino, D.M. Alba and an anonymous reviewer for their constructive comments, which greatly ameliorated this short paper.

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Manuscript received 5 July 2012

Revised manuscript accepted 2 August 2013 Published online 30 October 2013

uppeRCHeekteetH

M1 = length at occlusal level; M2 = length 10 mm above the tooth’s base; M3 = width at occlusal level; M4 = width 10 mm above the tooth’s base; M5 = crown height measured along the mesostyle; M6 = number of plications on the anterior face of the prefossette; M7 = number of plications on the posterior face of the prefossette; M8 = number of plications on the anterior face of the postfossette; M9 = number of plications on the posterior face of the postfossette; M10 = protocone length; M11 = protocone width.

loweRCHeekteetH

M1 = length at occlusal level; M2 = length 10 mm above the tooth’s base; M3 = length of metaconid-metastylid; M4 = length of the prefossette; M5 = length of the postfossette; M6 = width across plane of ectoflexid/linguaflexid ; M7 = width 10 mm above the tooth’s base; M8 = width across plane of metaconid and enamel band labial to protoconid; M9 = width across plane of metstylid and enamel band labial to hypoconid; M10 = crown height as measured from base to occlusal level on mesial face of the tooth.

metaCaRpal iii

M1 = maximal length; M2 = medial length; M3 = minimal breadth; M4 = depth of diaphysis at level of M3; M5 = proximal articular breadth; M6 = proximal articular depth; M7 = maximal diameter of the articular facet of the third carpal; M8 = diameter of the articular facet for the fourth carpal; M9 = diameter of the articular facet for the second carpal; M10 = distal maximal supra-articular breadth; M11 = distal maximal articular width; M12 = distal maximal depth of the keel; M13 = Distal minimal depth of the lateral condyle; M14 = distal maximal depth of the medial condyle.

Specimen # Site Species tooth side M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11

MSF 119 BRS H. malpassii P4 L 23.0 19.8 22.7 20.8 49.1 2 6 5 1 6.4 3.6 MSF 120 BRS H. malpassii P4 L 23.6 19.7 21.5 20.3 (47.0) 2 6 4 1 6.0 4.1 IGF 9400V BCB V3 H. malpassii P4 L 24.1 20.5 23.7 24.4 29.8 3 10 7 1 5.3 4.2 IGF 9406V BCB V3 H. malpassii P4 L 21.7 19.7 22.2 22.9 23.3 7 11 9 4 6.9 5.3 IGF 9408V BCB V3 H. malpassii P4 R 23.5 19.4 22.7 24.5 31.5 6 8 9 5 6.6 4.0 IGF 9413V BCB V3 H. malpassii P4 R 25.3 23.1 25.1 26.2 27.4 10 13 14 1 7.2 5.6 IGF 5286V BCB V3 H. malpassii P4 L 27.8 - 20.9 - - 2 2 3 - 4.5 4.0 NHMBJH126F BCB V3 H. malpassii P4 R 27.6 23.4 21.9 - 42.4 1 6 4 - 4.2 4.8 NHMBJH134 BCB V3 H. malpassii P4 L 27.7 23.6 22.1 25.3 44.3 1 6 4 - 4.0 3.6 NHMBJH229E BCB V3 H. malpassii P4 L 25.1 22.2 21.9 22.7 48.1 7 10 2 1 7.0 3.4

Specimen # Site Species tooth side M1 M2 M3 M4 M5 M6 M7 M8 M9 M10

MSF122 BRS H. malpassii M2 L 20.8 19.5 13.8 6.7 7.7 13.6 11.9 11.4 10.3 32.3

NHMBJH160E BCB V3 H. aff. malpassii M2 L 24.3 21.9 12.8 8.4 9.0 8.8 12.8 9.6 8.8 45.7 NHMBJH160M BCB V3 H. aff. malpassii M2 R 25.1 21.8 12.9 7.4 8.7 8.2 13.2 9.5 9.6 44.6 IGF9398V BCB V3 Hippotherium sp. M2 L 20.7 - 12.0 6.8 6.6 - 9.3 10.0 - -NHMBJH122A BCB V3 Hippotherium sp. M2 L 21.1 - 12.0 5.6 8.5 10.8 - 11.1 10.7 -NHMBJH122B BCB V3 Hippotherium sp. M2 R 21.0 - 12.0 4.7 6.4 11.3 - 11.2 9.8 -NHMBJH125C BCB V3 Hippotherium sp. M2 L 22.9 22.4 11.3 7.1 7.8 13.2 12.9 11.9 10.2 38.7 NHMBJH137 BCB V3 Hippotherium sp. M2 L 24.4 19.7 13.4 8.4 10.6 12.8 13.3 10.7 10.5 36.6 NHMBJH176A BCB V3 Hippotherium sp. M2 L 21.9 20.2 12.4 6.3 9.3 14.9 13.1 12.1 11.7 25.6 NHMBJH207 BCB V3 Hippotherium sp. M2 R - - 11.8 6.1 7.5 - - 11.1 - 27.3 NHMBJH216 BCB V3 Hippotherium sp. M2 L 21.3 20.9 11.4 6.7 9.3 11.0 12.5 9.7 9.0 32.4

Spec. # Site Species side M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14

MSF121 BRS H. malpassii L - - 26.9 22.9 (37.2) (27.8) (30.0) - - - - - -

-IGF8192V V3 H. malpassii L 214.3 206.2 27.2 21.5 39.3 25.1 30.6 14.4 6.1 37.5 35.0 27.9 24.2 25.6 IGF9397V V3 H. malpassii L 216.2 209.2 27.8 22.5 42.1 29.9 36.6 12.9 7.4 40.0 38.2 30.3 25.7 26.6

NHMBJH144 V3 H. sp. - - 29.9 23.4 - - -

-a

Measurements of Hippotherium from Monticino gypsum quarry, compared with Hippotherium sample from Baccinello V3 (approximate measurements between parentheses)